Properties of Solar Active Regions and Solar Eruptive

Properties of Solar Active Regions and Solar Eruptive Events Yang Liu -- Stanford University yliu@solar. stanford. edu September 2006 CISM All Hand Meeting

Outline Morphology patterns of active regions and solar eruptions; n Quantitative characteristics of active regions and solar eruptions; n More complex quantities of active regions and solar eruptions; n Summary. n September 2006 CISM All Hand Meeting

Morphology pattern n Morphology patterns of flare/CMEs-productive ARs: n n n Active regions not obeying Hale-law (e. g. Zirin 1988); δ-sunspots (e. g. Zirin 1988). Evolutionary characteristics of flare/CMEs-productive ARs: n n Emerging magnetic flux regions occur within pre-existing ARs (e. g. Hagyard et al 1985); Magnetic cancellation (e. g. Wang et al 1996); Related shear motion of magnetic features with opposite polarities along the neutral line (e. g. ref…); Collision of magnetic features with opposite polarities (e. g. Wang et al 1991? ). September 2006 CISM All Hand Meeting

Quantitative characteristics n Active regions with following characteristics are more flare/CMEs-productive: High magnetic shear along the neutral line (e. g. Hagyard et al, 1984); n High magnetic gradient toward the neutral line (e. g. Wang et al 2005); n Strong magnetic twist represented by force-free alpha (Falconer et al 2002)—actually can be presented by vertical electric current; n Length of the highly sheared, strong-field neutral lines (Falconer et al 2002; 2003, 2006); n Length of neutral lines with high magnetic gradient (Falconer et al 2003; Cui et al, 2006) n Effective distance of active region that is defined as the distance of center-of-gravity of opposite polarities normalized by the In summary, thesize measures describe properties of neutral active region (Guo etabove al 2006); CISM All Hand Meeting September 2006 line and magnetic field nearby. n

More complex quantities of ARs n Active regions with following properties are more flare/CME-productive. n n n Coronal bright loops appear to be much different from the potential field structure (Scherijver et al 2005): kind of 3 D magnetic shear angle; Many singular points on the photosphere (Cui et al 2006); Same sign of the magnetic twist and writhe in the active regions (Tian et al 2004); Large magnetic energy and helicity flux rate in the active regions (La. Bonte et al 2006); High relative free magnetic energy and high relative helicity in the active reions (Georgoulis et al, 2006). September 2006 CISM All Hand Meeting

Summary n An eruptive active region needs to possess sufficient free energy, and magnetic field of the active region needs to evolve toward an unstable state. What we need to learn are: n n n What we have learned from observations for an eruptive active region: n n Mechanisms and processes of free energy buildup; Processes of development of instability. Big-size region with high potential energy; Properties of main neutral line and magnetic field nearby; Evolutionary characteristics with dynamic behaviors (need to be more quantitatively characterized: it’s probably a key toward thoroughly understanding solar eruption and reliably forecasting space weather). Threshold values for some indexes are suggested to distinguish eruptive active regions and non-eruptive active regions, but need further investigation (more detail). September 2006 CISM All Hand Meeting